Centimeter wave detector



Sept. 9, 1947. w. L. CARLSON CENTIMETER WAVE DETECTOR Filed Oct. 26, 1943 ce z :,49

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WENDL LEHRLSUN l- Bg Gttorncg nventor Patented Sept. 9, 1947 CENTIMETER WAVE, -DE'rE-C'ron Wendell L. Carlson, Lawrenceville, JQ, assignor to Radio Corporation of America, a corporation of Delaware Application October 26, 1943,` Serial No.- 507,75`5

This invention relates vgenerally to centimeterV wave apparatus and more particularly to an improved method` of and means for supportinga centimeter wave crystal detector in operable relation within a waveguide transmission system.V

Tubular type crystal detectors employing silicon crystals, having a knife edge for contact with a tungsten catwhisken have been especially developed for high signal-to-noise characteristics andruniform operation at the super-high irequencies employed in waveguide transmission systems. The crystal is supported transverselyT within the waveguide by means of a suitable threaded clamping cap which provides electrical contact between one terminal of the tubular crystal detector and one of the wave-guide walls. It is customary to couple the remaining terminal of the tubular crystal detector to the opposite waveguide wall through a fixed capacitor.` ModulatiOn frequency currents are derived from the latter detector terminal while the microwavesignal components are effectively transmitted through the capacitor to the waveguide wall.

Considerable attenuation of the microwave signal components by the structure supporting the capacitor frequently is encountered due to the physicalA dimensions of the capacitor support which necessarily approach considerable fractions of the operating wavelength. The instant invention contemplates additional capacitive means integral with'the first capacitor support, whereby the microwave signal components suffer low attenuation between the second crystal contact and the adjacent waveguide wall. Furthermore, the capacitor supporting means is proportioned to provide an anti-resonant cavitywhich offers relatively high attenuation to the microwave signal components and relatively low attenuation to the modulation signal components derivedfrom the detector.

Among the objects of the invention are to provide an improved method of and means for detecting modulated microwave signals transmitted through a waveguide transmission system. An-

7' Claims.. (Cl. Z50- 31) erence to the accompanying drawing of which Figure 1 is a side elevational view cfa preferred embodiment, Figure 2 is a fragmentary bottom view of the embodiment shown in Figure l, `and Figure 3 is a schematic circuit diagram of the equivalent electrical circuit of the invention. Similar reference `characters are applied Vtoslml.- lar elements throughout the drawing.

Referring to Figures 1 and 2, one of the Walls I, of a rectangular waveguide 3, is apertured to receive a threaded cylindrical sleeve 5 for sup-- porting one terminal 1 of a tubular crystal detector 9 of the type described heretofore. A cylindrical conductive cap I I, threaded to engage the threads in the cylindrical sleeve 5, retains the detector terminal 1 in engagement with the cylindrical sleeve 5, thereby providing electrical conf tact betwen the detector terminal 1 and the waveguide wall I. A silicon crystal I3 is electrcally connected `to and supported by a. cylin.- drical projection I5 of the'detector terminal 1. The crystal I3 has avknife edge |1,which engages a tungstenwire catwhisker IS. The tungsten wire catwhisker I9 is supported by a second cylindrical detector terminal 2|. The cylindrical conductive members I5, 2|, and the crystal `I3 and catwhisker |9 .are enclosed within a glass, ceramic or suitably insulated sleeve 23. A cylindrical prong 25 projects coaXially from the outer` end of the second cylindrical supporting member 2|.

The'wall 2'1, of the waveguide `3, opposite the waveguide wall I, includes a threaded aperture for receiving'a second threaded sleeve 29 which surrounds the prong 25 and the second cylindrical terminal 2|. The penetration of the threaded sleeve 29 into the waveguide interior may be varied by rotation thereof in the threaded aperture in the waveguide wall 21. A ilexible contact ring 3|, suitably secured to the wall 21, provides uniform electrical contact between the second threaded sleeve 29 and waveguide wall 21. If Xed filtering is desired, the sleeve 29 may be fixed in position by soldering it to the waveother object of the invention is to provide an guide Wall 2"- improved supportV for a microwave detector in a waveguide transmission system. An additional object of the invention is to provide an improved network for coupling a crystal detector to a microwave waveguide transmission system.

Further objects of the invention include an improved adjustable lter network for coupling a crystal detector to a waveguide. A further object of the invention is to provide an improved method of and means for 'effectively segregat- 55 ring 33- Y K ment 45, electrically connected to the flat plate ing the carrier and modulation signal components derived from a crystal. detector effectively disposed within a microwave waveguide trans- `Vmission system.

The invention will be further described by ref- The second threaded sleeve 29 is terminated in an annular ring portion 33. A flat plate 35 ls separated from the annular ring 33 by a layer of mica, or other dielectric, 31 to provide a relatively large capacitor which is indicated in Figure 3 as thecapacitor C2, A terminal 39 provides an output connection to the flat plate 35 while a second terminal 4| and insulated bushing 43 provide an output terminal for the annular A flexible cylindraceous contact ele- 60.25, the second threaded sleeve 29, and the at plate 35 may be proportioned to be substantially anti-resonant to the microwave operating or carrier frequency.

It will be seen that the effective inductance LI provided by the prong 25 and the flexible contact element 45 may be varied by rotating the entire capacitor supporting structure within the threaded aperture in the waveguide wall 2`|. The eiective bypassing of microwave signal components derived from the detector is accomplished by a capacitor provided between the inner surface of the second threaded sleeve 29 andthe'outersurface of the conductive second cylindricaldetector terminal 2|. This capacitor is Cl of Fig.3 and also may be effectively variable simultaneouslywith the inductance LI by rotating the second; threaded sleeve v29 toprojectY more'or less of thefsleeve 29'into the interior 'of the wave- The output terminals 39, 4i may be connected to any desired modulation utilization circuit such as,Y for example, the primary winding 4'! cf'an intermediate 'frequency transformer TI. It should be understood that modulated microwave signals and unmodulated local oscillations both maybe introduced into the waveguide 3 to provide intermediate frequency modulated signals at the output terminals 39,41 of the capacitor C2.

Referring to Figure 3, the crystal detector 9 is illustrated as interposed in series between an impedance Zo, representing the waveguide characteristic impedance, and an impedance Tl, representing the output load impedance. The variable capacitor Cl, connected between the loadterminalj of the crystal and the common terminals of thewaveguide and load impedances, represents thev main bypass capacitor for the microwave signalcomponents passing through the crystal detector. The variable inductive element LI, corresponding to the inductanceinterposed by the center prong and contacts 25, 45, is eiectively connected in series with the crystal and one terminal of the load impedance Tl. The capacitor C2 is effectively connected directly across the load impedance Tl. The dash line 49 is indicative of the fact that the capacitor Cl and the inductor Ll 'are adjustable simultaneously. It will be seen that the network effectively connected between the crystal'detector and the load impedance Tl represents a low-pass filter having a relatively 50 large Ybypass capacitor CI on the input thereof for bypassing the microwave signal components. The Q of the filter network is relatively high, since thenetwork elements are essentially pure reactances.

Thus the invention described comprises an improved method of and means for coupling a crystal detector to a waveguide transmission system wherein microwave and signal modulation components derived from the detector are eiectively segregated by means of an adjustable filter network disposed in operable relation to one of the detector terminals.

I claim as my invention:

l. A detector network for a waveguide system including a crystal detector having a pair of terminals,means for supporting said detector transversely of said waveguide and providing contact between said waveguide and one terminal of said detector, first capacitive means coupling the remaining terminal of said detector to said waveguide, means dening amanti-resonant cavity disposed adjacent said first capacitive means and surrounding at leasta portionv of said remaining 4 terminal, second capacitive means integral with said anti-resonant cavity means, and means for deriving modulation signal currents from said detector.

Y 2. A detector network for a waveguide system including a cartridge type crystal detector having a pair of terminals, means for supporting said detector transversely of said waveguide and providing contact between said waveguide and one terminal ofv said detector, rst capacitive means comprising cylindrical conductive means concen- 'tric with a'p'ortionV of said detector for coupling v the remaining terminal of said detector to said waveguide, means dening an anti-resonant cavityl disposed adjacent said first capacitive means and surrounding at least a portion of said remaining' terminal, second capacitive means integral with said anti-resonantcavity means, and means for deriving modulation signal currents from said,

4. A detector network for a waveguide systemA including a crystal detector having a pair of terminals, means for supporting said detector transversely of said waveguide and providing contact betweensaid waveguide and one terminal of said detector, rst capacitive means coupling the remaining terminal of said detector to said waveguide, an anti-resonant circuit including an inductive element disposed adjacent said rst capacitive means and surrounding at least a portion of said remaining terminal, second capacitive means integral with said anti-resonant circuit and including contact means for engagement with said remaining detector terminal, and means for deriving modulation signal currents from said detector.

5. Apparatus 0f the type described in claim 4 characterized in that said modulation signal currents are derived from across said second capacitive means.

6. Apparatus of the type described in claim 4 including means for adjusting said first capacitivev means for varying simultaneously said inductive element and the coupling between said waveguide and said detector.

7. Apparatus of the type described in claim l including threaded means interposed between said cavity means and said waveguide for tuning said cavity means.

WENDELL L. CARLSON.

REFERENCES CITED The, following references are of recordin the le of this patent:

2,253,589 Southworth Aug. 2,6, 1941 

